I've had my Livewires for about 1 month. I had the same problem. On the same floor, they work at the maximum speed of the ISP plan I'm on (18 mbps). On different floors, they're at 3-10 mbps, plus intermittent connections*.
*On different floors, there are periods when they keep dropping, the PLC and Power light go on and off and my Network Magic program will constantly show my internet connection as Connected and then Disconnected. It's quite frustrating.
But, after finding this thread this morning, I'm given new hope!
It's interesting (if it's true) to learn that other electrical devices will affect it and that it self-optimizes.
Because normally, when I first get on my computer and the problem starts, I start tinkering with the Livewires.
However, today, I just put up with the intermittent connection and got on this message board for the first time. I only registered previously, and I didn't know my password and by the time I finished recovering my password, getting past the reCaptcha, and reading different threads on this board, my connection became stable!
I'm wondering if the initial powering on of the computer has an effect and it self-optimizes. Tomorrow, I start a new job, so I don't think I'll test and be able to post tomorrow morning, but, I'm going to test this out and just turn on the computer and leave the Livewires to see if they fix themselves after a period of time. It was probably 10-15 minutes of reading through this board when the connection stabilized. I'll report back to share the results.